A bizarre fight between the main pro-Kremlin parties returned to the political stage Wednesday when United Russia officials accused A Just Russia leader Sergei Mironov of conducting a "frenzied campaign" against the ruling party.

Analysts said that despite a Feb. 8 truce, the burgeoning rivalry was there to stay because of the very nature of both parties, created by the Kremlin to keep control of the political system.

The attacks centered on Mironov's remarks in an online interview with readers of the liberal Gazeta.ru news portal, in which he lambasted Clean Water, a tap water purification project sponsored by United Russia leader Boris Gryzlov.

Mironov called the project's engineer, self-styled inventor Viktor Petrik, a charlatan and questioned Gryzlov's trust in him.

Gryzlov and Petrik filed a patent for a water filter in 2007 that they say turns radioactive water into pure drinking water.

Andrei Isayev, a senior United Russia official who chairs the State Duma's Labor and Social Policy Committee, said Mironov had unleashed "a frenzied campaign against United Russia" and suggested that A Just Russia was supporting producers of bottled water.

"United Russia won the March 14 elections. But now some of the losers — an aggressive minority — are trying to impose their will on the majority," Isayev told a Duma plenary session, according to a transcript posted on his party's web site.

"Producing, bottling and selling water undoubtedly is a very profitable business. … This business will be undermined when each family can drink clean tap water," he said.

United Russia Deputy Ruslan Kondratyev accused Mironov of being a greedy fat cat. "You get the impression that he does not understand his own words lately," he said in comments released on the party's web site. "You can compare such frenzied criticism with those fat cats interested only in lining their pockets and never thinking about people's welfare."

Isayev also repeated an earlier comparison of Mironov to an evil character in Slavic folklore. "Like Koshchei the Immortal, he sits on water bottles," he said.

Mironov hit back on Wednesday by calling United Russia leaders fairy-tale dimwits — echoing his remarks during a previous dispute. "Those Ivan the Fools are not calming down — and I stress fools," he told reporters in St. Petersburg, Interfax reported.

United Russia's "stubborn support for charlatans" is shameful, he said. "This is nothing holy but a desecration and a scam that stinks. Instead of being clean there is just muddy water," Mironov said.

The renewed war of words comes almost two months after Mironov prompted a stream of vitriol from United Russia by saying he disagreed with Prime Minister Vladimir Putin, who is United Russia's chairman, over the 2010 budget and anti-crisis measures.

On Feb. 8, Mironov and Gryzlov signed a joint declaration in which both promised to "act in a coalition to solve the country's most pressing problems." Each heads a house of parliament: Gryzlov is Duma speaker, while Mironov heads the Federation Council.

United Russia commands a two-thirds majority in the Duma and boasts similar dominance throughout the country. A Just Russia has the smallest Duma faction with 8 percent of the seats.

Tatyana Stanovaya, an analyst with the Center of Political Technologies, said bipartisan rivalry was unavoidable because United Russia and A Just Russia compete for administrative resources.

"Ever since A Just Russia was formed in 2006, United Russia has seen it as a serious enemy. There can only be one party of power," she told The Moscow Times.

Stanislav Belkovsky, an independent political analyst who was a Kremlin insider when A Just Russia was formed, said the current bickering was also a consequence of Putin's withdrawal from the Kremlin.

"When Putin was president, attacking United Russia was an offense. Now you can do it because he is no longer the king," he said.

The disputes between Mironov and Gryzlov have attracted much mockery because both have a reputation for being among Putin's strongest loyalists from his native St. Petersburg.

Asked in the Gazeta.ru interview if it would be a good idea to gain real popularity by appearing as a clown in a circus, Mironov replied dryly: "Why do you dislike the circus so much?"